Apparatus for converting currents



Jan. 30, 1940. F. KOPPELMANN 2,188,361

APPARATUS FOR CONVERTING CURRENTS Original Filed Oct. 5, 1937 2Sheets-Sheet l Jan. 30, 1940. F. KOPPELMANN APPARATUS FOR CONVERTINGCURRENTS Original Filed. Oct. 5, 1937 2 Sheets-Sheet 2 Patented Jan. 30,1940 UNITED STATES PATENT OFFICE Floris Koppelmann, Berlin-Siemensstadt,Germany, aaaignor to Siemena-Schuckertwerke Aktiengeselischait,

Berlin-Siemensstadt,

Ger-

y, a corporation oi Germany Application October 5, 1937, Serial No.167,422. Renewed May 2, 1939. In Germany October 5, 1936 i 24 Claims.

The present invention relates to an apparatus for converting singlephase or polyphase alternating current into direct current or viceversa, or single phase or polyphase alternating current into alternatingcurrent of another frequency by means 01' periodically operatedmechanical contacts. Such an apparatus is described in the copendingapplication Serial No. 114,965, filed on December 9, 1936. An apparatusof the abovementioned character differs from the known apparatus ofsimilar type by the use of means for simultaneously influencing thecurrent and the voltage across the switching gap of each phase. Thesemeans consist of a current distorting impedance connected in series withthe switching gap, and of a current path connected in parallel relationto the make and break contacts. Some particularly advantageous types ofsaid means will be hereinafter described, and others which may also beused in connection with the present invention form the subject matter ofthe following copending applications: Serial No. 122,232, filed onJanuary 25, 1937; Serial No. 129,987, filed on March 10, 1937; SerialNo. 128,185, filed on February 27, 1937; Serial No. 125,363, filed onFebruary 12, 1937; Serial No. 133,758, filed on March 30, 1937.

The purpose of the simultaneous influencing of the current and voltageis to suppress the arcing when opening the make and breakcontacts byautomatically causing the current to assume substantially the zero valueshortly before the beginning of the opening of the contacts and tomaintain the zero value for -a certain interval while the contacts areopened, whereas the current interrupted at the make and break contactsis at least partly maintained through the parallel path in such a mannerthat the voltage drop of the circuit to be interrupted is applied atfirst substantially to the impedances connected in series to the makeand break contacts and that a great average operating current and a highaverage operating voltage, are not any more stressed at the moment atwhich the contacts are broken than in the caseof a weak current systemin which currents of the order of magnitude of 1 ampere or less flow orin which an operating voltage of the order of 10 volts or less ispresent.

A particularly advantageous means for attaining the above-mentionedautomatic distortion of the current is a so-called switching reactorwhich is series-connected to the make and break contacts. Such aswitching reactor is also described in the above-mentioned copendingapplication Serial No. 114,965. It consists oi an inductance coil whoseiron core consists of a particularly high-graded ferromagnetic ironalloy of extreme permeability and of extremely great saturationinduction, which iron is suddenly saturated with increasing current uponexceeding a predetermined current value, as is manifested by arelatively sharp saturation bend of its magnetization curve. The numberof turns of the coil is so chosen that the coil is unsaturated only atvery small instantaneous values of the current in the neighborhood ofthe zero value and is saturated already upon exceeding an instantaneousvalue of the current of the order of one thousandth or of oneten-thousandth of the normal average operating current. The resistanceof such a reactor is very small in the saturated state. It permits,therefore, in the state of saturation the passage of the normaloperating current during the greatest portion of each period duringwhich the current flows without appreciably impeding thiscurrent.However, as soon as the reactor, owing to the decrease of the currentbelow a predetermined value, is' suddenly desaturated while the currentaccording to the descending portion of its curve approaches the zerovalue, the resistance of the reactor assumes almost instantaneously avery high value which is several thousand times greater than theresistance in the saturated state. Consequently, the current flowingthrough the reactor during the period .of the desaturation is greatlyimpeded and there occurs a weak current interval during which thecurrent intensity has ,a negligible value, i. e., is practically zero.The reactor must be so dimensioned that this interval is of the order ofa millisecond. During this time the contacts may be broken without thereoccurring any arcing, if as a result of a suitable dimensioning of thecurrent path parallel to the contacts care is taken to increase therestriking voltage only slowly. The resistance of the parallel path mustbe so rated that it amounts only to a fraction of the resistance or thereactor in the unsaturated state;

' the contacts.

then the total voltage of the circuit distributes itself in proportionto the said resistances over the switching gap and the reactor, providedthat all other resistances may be neglected. The total voltage of thecircuit is therefore almost exclusively applied to the reactor in theunsaturated state.

By an auxiliary winding on the magnet core of the reactor, the lattermay be biased additionally opposite to .the direction of the operatingcurrent to be transmitted in such a manner that the desaturation of thereactor occurs already while the operating current varies according tothe descending portion of its current curve and still has a positiveinstantaneous value, i. e., before the operating current passes throughits zero value. The additional magneticbias may be efiected with the aidof direct current or by an alternating current which has the samefrequency as the alternating current to be converted and whose positionof .phase is adjustable with the aid of an induction regulator or thelike in such a manner that the magnetic bias has at the desired momentbefore the breaking of the contacts the desired direction opposite tothe direction of the operating current.

The present invention relates to improvements of converting apparatus ofthe above-outlined type, and especially refers to the switching-inoperation of the contacts. The nature of these improvements will beapparent from the following considerations.

The above-mentioned means for simultaneously influencing the current andthe voltage may under certain circumstances cause relatively largecurrents to occur when switching in the make and break contacts. Theselarge currents may be due to the fact that the switching reactor--whichwhen being switched out is unsaturated and has a very highresistance-may under certain conditions be just in the state ofsaturation when being switched in and therefore have a very smallresistance. A further reason for the occurrence of large currents at theswitching in moment is that the condensers connected in parallelrelation to the make and break contacts are discharged when switchingin. Furthermore, relatively high voltages may occur across the switchinggap shortly before the engagement of Consequently, an arc may beproduced when switching in, which carries immediately a current ofrelatively high intensity, whereby the contacts may be damaged andbecome useless after a relatively short operating period. Such damagesare the more likely, if the contacts are made of good conducting metals,such as silver, copper or the alloys thereof for the purpose of reducingthe voltage losses during the period of the current fiow. In series withthe parallel-connected condensers, high-ohmic resistors could beconnected by which the discharge current of the condensers is maintainedsmall. The resistance of such resistors would, however, be so great inthis case that the restriking voltage when switching out may not besufficiently reduced and consequently the danger of an arcing now wouldbe increased when switching out.

The main object of the present invention consists in preventing thecreation of large currents or current surges at the closing moment ofthe contacts when switching in the circuit breakers.

A further object of the invention consists in reducing the voltageexisting across the switching gap immediately before the closing momentof the contacts in such a manner that a sparking cannot take placebefore the closure of the contacts.

According to the invention an additional reactor is employed inconnection with every circuit breaker to which a switching reactor isconnected in series. This additional reactorhereinafter referred to asswitching-in reactor is so arranged that it lies shortly before and whenswitching in the circuit breaker in a circuit which includes in seriesthe make and break contacts, the condenser of the parallel path and theswitching-in reactor. The switching-in reactor has also an auxiliaryexciting winding by means of which it is so biased with direct currentor alternating current that it is magnetically saturated when switchingout i. e., the switching-in reactor has a low resistance for the currentflowing therethrough when switching out, whereas it is unsaturated whenswitching in so that it has a high resistance for the currentflowingtherethrough at the switching-in moment.

For a better understanding of the present invention reference may bemade to the accompanying drawings in which Fig. 1 shows a three-phaseconverting apparatus, the fundamental total connection according to theabove-mentioned copending application Serial No. 114,965 being shownschematically while the switching apparatus is illustrated more indetail.

Figs. 2 to 4 show three different forms of the invention in which forthe sake of simplicity only that portion of one phase is indicated whichmanifests the inventive improvements, whereas the mechanical portion ofthe converting apparatus is shown schematically. The part circuits shownmay be employed in a single phase system or may be according to Fig. 1combined to arrangements of any number of phases.

Fig. 4a shows a modified detail of Fig. 4.

Fig. 5 shows in detail the contact device of the arrangement accordingto Fig. 4 on an enlarged scale.

The arrangement according to Fig. 1 consists of four main groups ofparts, namely the power source I which supplies the converting apparatuswith three-phase alternating current through an intermediatetransformer; the switching device 2 which is equipped with an adjustablesynchronous drive; the device 3 for influencing the voltage and thedevices 4 for influencing the current.

To the supply circuit fed by the power source I are connected the inputterminals IIII, I02, I03 of the primary windings III, H2, N3 of atransformer whose secondary windings are designated by the numerals I2l,I22, I23. The secondary winding is star-connected. The neutral point isconnected to the current consuming device 2") through a conductor. Fromthe free terminals of the windings I2I, I22, I23 extend the mainconductors to the switching reactors 304, 3, 324 which are wound on themagnet cores 305, 3I5, 325. The cores are provided with auxiliaryexciting windings 3I'I, 3I8, 3I9 which are biased by a direct-currentsource (battery) I9I. In the biasing circuit is inserted a rheostat 360which permits adjusting the magnitude of the biasing current to thedesired value depending upon the operatirg conditions. Furthermore, inthe direct-current circuit is inserted a reactance coil 36l whichprevents the pulsations of current which might be caused by theinductive coupling of the biasing coil with the main coils of the Tl ofthe secondary windings I2I, I22, I23.

switching coils from reaching the direct-current source.

From the switching coils extend main conductors to each of the make andbreak contacts I4I. I42, I43 which are arranged in pairs. The latter areplaced on the intermediate plate I20 of an insulating frame I90. Eachstationary contact pair cooperates with a movable contact I5I, I52, I53which in the closed position bridges the make and break contacts and isunder the influence of a spring I1I, I12, I13 respectively which in turnpresses against a cross bar I30 of insulating material. The main currentcircuit extends from the second contact of each contact pair to a commonconductor I45 which forms the other pole of the current consuming device2I0 and in which is inserted a smoothening inductance coil II4.

To the make and break contacts are parallelconnected the current pathsII5, I25, I35 respectively which may consist of ohmic or inductive or ofcapacitive resistor units or of any combination of such resistor unitsand which under certain conditions may be provided with the additionaldevices hereinafter described in connection with Figs. 2 to 4.

The movable bridge contacts I5I, I52, I53 perform in operation an upwardmovement which is brought about by tappets IGI, I62, I63 consisting ofinsulating material. The latter are under the influence of a spring I1I,I12, I13 respectively and are operated by cams I8I, I82, I03 which arefirmly mounted on a shaft I08 and angularly displaced by 120 withrespect to one another. The shaft I08 is mounted in the frame I90 and isdriven by the synchronous motor I06 through an intermediate couplingI01. The synchronous motor is connected to the secondary winding 226 ofan induction regulator whose primary side is connected to the outputterminals The induction regulator'serves to vary the phase position ofthe rotating field of the driving motor I06; in this manner the momentsat which the contacts are closed and opened are so adjusted that theopening of the contacts always occurs during the above explained weakcurrent intervals in the neighborhood of the zero value of the currentto be interrupted. On the shaft I08 are further arranged auxiliarycircuit breakers 90 operating with current collectors (brushes) 95 whichare held by supports 99 secured to the intermediate plate I20. Thepurpose and the op eration of the last-mentioned auxiliary circuitbreakers are hereinafter described in connection with Fig. 4. By thesimultaneous adjustment of the biasing current with the aid of therheostat 300 and of the moments at which the contacts are opened andclosed with the aid of the induction regulator 6, I26 a control of thecurrent and the voltage may also be attained within wide limits (of. theabove-mentioned copending application Serial No. 122,232),

In Fig. 2, 304 denotes the switching reactor with the magnet core 305and the auxiliary biasing winding 3I1 which is connected to thedirectcurrent source I3I through the rheostat 360 and the reactor 35LThe main conductor extends from the switching reactor 304 throughcircuit breaker 2 to the conductor I45 leading to the current consumingdevice 2I0 (not shown in Fig. 2).

In parallel relation to the make and break contacts lies as abovementioned an impedance arrangement II5. This arrangement consists of acondenser l and a low-ohmic resistor I5. In

the parallel path is further inserted an auxiliary switching reactor 504which need only be rated for a small current, since the currents flowingthrough the parallel path amount to a fraction of the main current oronly flow for a very short time. The magnet core 505 of the reactor 504is also provided with a biasing winding denoted by the numeral 5H andconnected to a battery '92 through a rheostat 560 and a reactor 56I. Thedirection of current of the magnetic bias is so adjusted as to exert amagnetic action in the same direction as the current flowing into thecondenser I5 when opening the contacts. The magnitude of the excitingcurrent is so adjusted that the core 505 of the switching-in coil isjust saturated if no current flows in the main winding 504. Thedischarge current created when closing the contacts flows in theopposite direction through reactor 504 and counteracts the dlrectcurrent magnetic bias. Consequently, the reactor becomes unsaturatedshortly before the moment at which the contacts of breaker 2 are openedand assumes therefore a high resistance. The high inductive resistanceprevents the capacitive discharge current from increasing until thecontacts are firmly closed. In order to maintain the inductance of thereactor in the saturated state; i. e., the air inductance of its windingas small as possible very high-graded iron of very high permeability ispreferably employed for the core 505 'of this auxiliary switching-inreactor as well as for the core 305 of the main switching reactor inorder to reduce the number of turns to a minimum. As stated above withrelation to the main switching reactor, such ferromagnetic material ofextremely high permeability is employed, the characteristic of which hasa sharp saturation bend.

Since for purely geometrical reasons it is difficult to attain a valuebelow a predetermined limit value for the air inductance of theauxiliary switching-in reactor it is advisable to connect two or, ifdesired, also various of such switchingin reactors in parallel relationwith one another in such cases where a very small air inductance, i. e.,a very small resistance is required for the current flowing in thecharging direction. To this end, a second auxiliary switching reactor504a with the core 505a and the biasing winding 5I1a is provided in Fig.2. The biasing windings BH and 5I1a are connected in series.

This arrangement may be advantageously employed not only in the manneras shown in the embodiment of Fig. 2 but also represents a valuableimprovement in all switching devices of any arrangement, such as is, forinstance, the case with rectifiers and inverters of difierent types,highly sensitive regulators and relays to which a condenser is connectedin parallel relation for facilitating the switching out operations.

In the embodiment shown in Fig. 3 an auxiliary switching reactor 504 isnot arranged in the parallel path but directly in series with thecircuit breaker 2. The iron core 605 of this auxiliary switching reactoris provided with two auxiliary exciting windings H1 and M10. Theexciting winding BI1 is fed by the battery I03 through a rheostat 650and a reactor 65L The exciting winding 6I1a, is connected to analtermating-current source I95. The latter must have the same frequencyas the alternating current taken from the main transformer. The excitingwinding 6I1a may, for instance, be directly connectedif desired, throughan auxiliary induction regulator 664 serving to accurately adjust theproper position of phase-to one of the secondary windings of the feedingmain transformer itself which has the suitable position of phase forthis purpose. Furthermore, in the auxiliary exciting circuit lies arheostat 853 and another auxiliary switching reactor 104 with aniron'core 105. This auxiliary switching reactor 104 need only be ratedfor a very small current. Its iron core 105 has an additional excitingwinding H1 which is fed from a battery I84 through a resistor I60 and areactance coil IN.

The current flowing in the exciting winding BI! is so adjusted that thecore 605 is biased in the opposite direction as by the main current. Themagnitude of this exciting current is so adjusted with the aid of therheostat 660 that the state of saturation is nearly attained by thebiaseifected by winding 6H alone. If the main current begins to flowshortly after the contacts have been closed the switching reactor 604has a very high resistance and consequently maintains the current at alow value until the state of saturation is attained when the currentflows in the opposite direction. The exciting winding 6lla is noteiIective during this interval, for the magnitude and direction of thebiasing current in the winding 1 l1 and the magnitude and phase positionof the alternating current taken from the power source I85 are so chosenthat the core 105 is unsaturated shortly before the closure of thecontacts 2 so that the auxiliary switching reactor I04 has a very highresistance and the current flowing therein and therefore in the windinglil'la is practically zero. However, as soon as the contacts are closedthe core 105 attains the state of saturation. In this manner theresistance of the switching coil 104 drops to a very low value. Theswitching reactor 104 permits therefore substantially without anyhindrance the passage of the alternating current taken from the powersource I95. The magnitude and the position of phase of this alternatingcurrent is so chosen that it exerts a magnetic effect. on the core 605in the same direction as the main current in the switching reactor 604.The switching reactor 604 is therefore rendered ineffective by thealternating current during the period of the flow of current proper andduring the time the main'contacts 2 are being separated.

In order to reduce also the voltage across the make and break contactswhen switching in, a special parallel path is provided as shown in theembodiment according to Fig. 3 in which is inserted a low-ohmic resistor624 and which is controlled byan auxiliary contact device 620. Thisauxiliary contact device consists of two stationary contacts 6 and arevolving part 65I which is driven in synchronism with the driving shaftfor the main contact device and is so adjusted that it closesa parallelcircuit shortly before the main contacts close. Since the auxiliarycontact device 620 has only to carry a very small current momentarilyand since a good contact is not essential insofar as also in the case ofa relatively bad contact the resistance of the parallel path is alwaysso small as to be neglected with respect to the resistance of theauxiliary switching reactor 4 which is at the same time in anunsaturated state, a slight consumption of the auxiliary contact device620 may be put up without impairing the normal operation of theconverter. Furthermore, the auxiliary contact may be made of a,materialwhich is particularly resistant to arcing; for instance of tungsten. Forthe above-mentioned reasons it the main contacts.

As soon as the parallel path is closed by the auxiliary contact device620, the total voltage distributes itself over the contact device 2 'andthe auxiliary switching reactor 604 according to the ratio of theresistance of the parallel path in which the resistor 624 and theauxiliary switching device 620 are inserted, to the resistance of theauxiliary switching reactor 604 which is in an unsaturated state. Sincethe resistance of the parallel path amounts only to a fraction of theresistance of the unsaturated auxiliary reactor the voltage across themain contacts shortly before their closure is so small as to beneglected. An arcing will therefore not occur at the main contacts.

Also in the embodiment shown in Fig. 4 the auxiliary switching reactor604 is connected in series with the interrupting device 2 and both arebridged by the parallel path through the resistance combination I I5consisting of an ohmic resistor l5 and a condenser IS. The iron core 605of the auxiliary switching reactor 604 carries an auxiliary winding 6"for effecting a magnetic bias. Winding 6|! is energized by the powersource l83 through a reactor 66l and a rheostat 660. The magnetic biasis soadjusted that shortly before the engagement of the contacts l4l,Mia and IN the core 605 of the auxiliary switching reactor is in anearly saturated state opposite to the direction of the main currentwhich begins to flow through the auxiliary switching reactor 604 afterthe closure of the contacts. This main current therefore maintainspractically the zero value until it has reversed the magnetization ofthe iron core and until the state of saturation is attained in the otherdirection. Only in this case themain current may flow through reactor604 without hindrance. In order to maintain also the voltage between thecontacts at a low value shortly before the engagement of the contacts, afurther parallel path is directly parallel connected to the contacts Iand I a, the resistance of this parallel path being small compared tothe resistance of the auxiliary switching coil 604 which is at thismoment in an unsaturated .state. The parallel path consists of adischarge tube 820 whose grid "I is connected through a high-ohmicresistor 82! to an auxiliary contact 24!, the closure of which leads.The .grid MI is biased by a battery I81 through a high-ohmic resistance823. The cathode is heated by a heating battery I98. A protectiveresistor 824 is connected in series with the discharge tube 820. Insteadof the resistance 824 also a condenser MS with a parallel-connectedresistor 824 may be series-connected to the discharge tube. Anotherswitching reactor 804 may be arranged in the lead to the discharge tubein order to protect the tube against a danger ous over-current. The ironcore 805 of the reactor 804 is provided with an additional biasingwinding 8|! which is energized by the direct current source l86 througha reactor "I and a rheostat 860. The magnetic bias is effected in adirection opposite to the direction of the current flowing normallythrough the discharge,

tube. The magnitude of the biasing current is so adjusted that theauxiliary switching reactor 804, 805 is highly saturated and permits thecurrent to flow in normal operation through the discharge tube 820without exceeding the saturation point In cases where considerablygreater currents may occur which would stress and destroy the dischargetube the auxiliary switching reactor 804, 805 comes within the workingrange below the saturation so that such dangerous currents are preventedby the high inductive resistance of the unsaturated auxiliary switchingreactor 804. If as above mentioned a condenser 8I5 with aparallel-connected ohmic resistance 824 is arranged in series with theauxiliary switching reactor 804 the condenser protects also thedischarge tube even if themagnetization of the auxiliary switching coil804, 805 has attained the saturation point in the opposite directionafter reversal by the interfering current. The auxiliary reactor 804,805, therefore, may be dimensioned smaller, as if the condenser 8I5 andthe parallel resistor 824 were not available.

A resistor 808 having a high resistance may be parallel-connected to theauxiliary switching reactor 804 in order to facilitate the equalizationof the magnetic energy when reversing the magnetism thereof.

The grid bias of the discharge tube 820 is adjusted to such a high valuethat the flow of current therethrough is prevented so long as theauxiliary contact 24I is not in engagement 7 with the movable contactI5I. The latter is connected to the stationary contact I4Ia by aflexible auxiliary conductor. As soon as it engages the preliminarycontact 2 the grid inverse voltage will be reduced. The discharge tube820 allows therefore a current to flow therethrough. Consequently, thevoltage at the main contacts HI and I4Ia drops substantially to a valueequal to the sum of the ignition voltage of the discharge tube 820 andof the voltage drop in the protective devices M5, 824, 804 and 808. Thisresidual voltage across the contacts amounts only to a fraction of thetotal voltage which is substantially applied to the auxiliary switchingreactor 604 being just unsaturated at this moment. Owing to the smallresidual voltage across the switching gap an arcing cannot occur acrossthe contacts MI and I5I.

An advantageous arrangement of the leading auxiliary contact 24I isillustrated in Fig. 5 in which the contact device shown in Fig. 4 isillustrated on an enlarged scale. The contact device consists as shownin Fig. 1 of the stationary contacts I4I, I4Ia secured to the insulatingplate I20. The movable contact I5I is under the influence of the springI'II which presses against a second insulating plate I30. The drive isbrought about by'the tappet IBI. The terminals for the leads are denotedby the numeral 245. The stationary contact MM is provided with a bore242 in which moves the pin contact 2. The contact pin has a collar 246and may be moved within a piston-shaped sleeve 243. The movement withinthis sleeve is limited by a stop 259 and an inner nut 240 which isadjustable by means of a fine thread 241. The collar 246 is pressedagainst the adjusting nut 248 by a spring 249. Upon the downwardmovement of the tappet I6I and the movable contact I5I the pin contact24I is pressed down against the force of the spring 249. Thepiston-shaped sleeve 243 is movably arranged within a second sleeve 244which is secured to the insulating plate I by means of an angleiron.254. The outer sleeve 244 is closed at both ends by covers 252 and253 consisting of insulating material and being each provided with abore. The bore of the cover 253 serves as'a guide for the contact pin24I. Between the lower cover 252 and the piston-shaped sleeve 242 isarranged a weak spring 25I which tends to press the sleeve 242 in theupward direction. The movement is, however, damped by the air above thesleeve 243 and is limited by the engagement of the collar 245 of thecontact pin 2 with the stop 259 upon the closure of the contacts. Thepiston-shaped sleeve 243 may therefore move in the upward directionduring the operating period only gradually by the same amount as theupper end of the auxiliary contact 24I wears off with time. In thismanner the contact pin 2 is automatically readjusted during theoperating period by such an amount that its upper end projects beyondthe contact surface of the stationary contact I4|m always the samelength when opening the contacts. The length of this portion of the pinmay be so adjusted with the aid of the adjusting nut 248 that the timeinterval which elapses between the engagement of the auxiliary contact 2and the movable contact I5I and that of the movable contact I5! and thestationary main contact 14!, has the desired value. This value ismaintained constant during the operation owing to the automaticadjustment by the spring 25I.

A conductor 25'! extends through the bore of the lower cover 252 fromthe contact pin 24I to the terminal-258. Another auxiliary conductor251a extends from the movable contact I5I to the stationary contactI4Ia. Both auxiliary conductors carry only the current flowing in thegrid circuit of the discharge tube 820 and are therefore very thin.

Furthermore, in Fig. 4 is provided a device by which the auxiliaryswitching reactor 604 is' short-circuited during the period of flow ofcurrent proper. This device consists of a contact device driven insynchronism with the shaft and of the brushes which are connected to theends of the reactor 604 through conductors. The contact device 90consists of two segments 9| which are directly connected to each other.Adjacent to each of these segments are arranged two short segments inthe direction of rotation which are connected to the bridging segments9| through the resistors 96 and 91. The short-circuit of the switchingreactor is therefore not suddenly eliminated but a resistance is atfirst gradually inserted in the bridging short-circuit connection. Inthis manner the interruption of the short-circuit connection is renderedas sparkless as possible. Instead of connecting the short-circuitconductor of the brushes 95 directly to the ends of the auxiliaryswitching reactor 604 the latter may be provided according to Fig. 4awith an additional short-circuit winding 606 having a slight leakage towhich the bridging contact device 90, 95 is connected.

As shown in Fig. l the revolving contact device 90 is mounted on thesame shaft I08 as the driving cams for the contact device. The supports99 for the brushes 95 are secured to the plate I20 of the insulatingframe I90.

The invention may be embodied in other forms than those shown anddescribed without departing from the scope of the invention.

What is claimed is:

1. An arrangement for converting alternating current into direct currentor vice versa, or alternating current of one frequency into alternatingcurrent of another frequency, comprising a switching device havingmechanically operated make and break contacts, means for simultaneouslyinfluencing thecurrent and voltage across the switching gap, said meanscomprising a switching reactor series-connected with said make andbreakcontacts and designed to abruptly increase its impedance at smallinstantaneous values of the current in the neighborhood of its zerovalue, and a voltage-biasing impedance path parallel-connected to saidmake and break contacts for reducing the operating voltage recurringbetween said contacts, in combination with a variable auxiliaryinductance designed to have a high resistance when switching insaid'make and break contacts, said inductance being seriesconnected in acircuit including said make and break contacts and said parallel path.

- 2. A current converting arrangement comprising a switching devicehaving mechanically operated make and break contacts, means forsimultaneously influencing the current and voltage across the switchinggap, said means comprising an inductance coil series-connected with saidcontacts and having a magnetic core designed to become abruptlyunsaturated at current intensities near the zero value and of a currentpath including capacitors arranged in parallel to said make and breakcontacts for reducing the operating voltage recurring between saidcontacts, in combination with an auxiliary switching-in reactorconnected in series with the make and break contacts in the circuitincluding said contacts and said parallel path, said switching-inreactor having a magnet core designed to be unsaturated only at smallinstantaneous current values in the neighborhood of the zero value andto become saturated upon the instantaneous current exceeding a givenvalue which amounts to a fraction of the mean current carried by saidswitching-in reactor in the state of saturation.

3. A current converting arrangement comprising a switching device havingmechanically operated make and break contacts, means for simultaneouslyinfluencing the current and voltage across the switching gap, said meanscomprising a current-biasing reactor series-connected to said make andbreak contacts and a voltage-biasing current path parallel-connected tosaid make and break contacts for reducing the operating voltagerecurring between said contacts, in combination with an auxiliaryswitching-in reactor connected in series with said make and breakcontacts in the circuit including said make and break contacts and saidparallel path, said switching-in reactor having a magnet core designedto become abruptly unsaturated upon the lowering of the instantaneouscurrent intensity to values in the neighborhood of the zero value, abiasing winding arranged on the core of said switching-in reactor, and abiasing circuit connected to said winding, said circuit including anauxiliary current source and variable means for controlling the magneticbias effected by said winding.

4. A current converting arrangement comprising a switching device havingmechanically operated make and break contacts,'means for simultaneouslyinfluencing the current and voltage across the switching gap, said meanscomprising a current-biasing reactor series-connected to said make andbreak contacts and designed to periodically increase its reactance atlow current intensities, and a voltage-biasing current path parparallelpath, said switching-in reactor having a magnet core designed to becomeabruptly unsaturated upon the lowering of the instantaneous currentintensity to values in the neighborhood of the zero value, a biasingwinding disposed on the core of said switching-in reactor, a biasingcircuit connected to said winding, an alternating current source havingthe frequency of the current to be interrupted by said contacts, saidsource being connected in said biasing circuit, and means in saidcircuit for controlling the phase position of the biasing current withrespect to the phase position of said current to be interrupted.

5. A current converting arrangement comprising a switching device havingmechanically operated make and break contacts, means for simultaneouslyinfluencing the current and voltage across the switching gap, said meanscomprising 4 a current-biasing reactor series-connected to said make andbreak contacts and designed to periodically increase its reactance atlow current intensities, and avoltage-biasing current pathparallel-connected to said make and break contacts for reducing theoperating voltage recurring between said contacts, in combination withan auxiliary switching-in reactor connected in series with said make andbreak contacts in the circuit including said make 'and break contactsand said parallel path, said switching-in reactor having a magnet coredesigned to become abruptly unsaturated upon the lowering of theinstantaneous current intensity to values in the neighborhood of thezero value, a biasing winding arranged on the core of said switching-inreactor, and an energizing circuit connected to said winding, saidcircuit being so adjusted that said switching-in reactor is in the stateof saturation upon the opening of said break and make contacts.

6. In combination with a device for closing and opening an alternatingcurrent circuit, a switching reactor having an inductance windingseriesconnected with said device so as to be traversed by thealternating current to be'controlled by said device and a magnet coredesigned to be uncore, a second switching reactor having a main windingconnected with said auxiliary biasing winding of said first reactor anda magnet core also designed to be unsaturated at said smallinstantaneous current intensities and saturated upon exceeding apredetermined intensity amounting to a fraction of the normal meanoperating current flowing through said main winding of said secondreactor, a biasing winding disposed on the core of said second reactor,and an energizing circuit connected with said latter biasing winding,said energizing circuit being adjusted to cause said second reactor tohave in a iven interval within each cycle of said alternatn current anincreased inductive resistance so that in said interval the auxiliarybiasing current controlling said first reactor has a minimum value.

'7. A current converting arrangement comprising a switching devicehaving mechanically operated make and break contacts, means forsimultaneously influencing the current and voltage across the switchinggap, said means comprising a self-saturating switching reactorseriesconnected to said make and break contacts for decreasing thecurrent intensities in the neighborhood of the passage of the currentthrough its zero value and voltage-biasing means connected in parallelto said make and break contacts and being provided with a variableauxiliary impedance designed to have an increased impedance value whenswitching in said make and break contacts, and an auxiliary contactdevice for bridging said auxiliary impedance during a given intervalwithin each current cycle, said interval including at least the'periodof the opening oi said contacts.

8. A current converting arrangement comprising a switching device havingmechanically operated make and break contacts, means for simultaneouslyinfluencing the current and voltage across the switching gap, said meanscomprising a self-saturating switching reactor series-connected to saidmake and break contacts for decreasing the current intensities in theneighborhood of the passage of the current through its zero value andvoltage-biasing means connected in parallel to said make and breakcontacts and being provided with a variable auxiliary impedance designedto have an increased impedance value when switching in said make andbreak contacts, an auxiliary contact device for br dging said auxiliaryimpedance, and means for operating said auxiliary contact device.

9. A current converting arrangement comprising a switching device havingmechanically operated make and break contacts, means for simultaneouslyinfluencing the current and voltage across the switching gap, said meanscomprising a self-saturating switching reactor series-connected to saidmake and break contacts for decreasing the current intensities in theneighborhood of the passage of the current through its zero value andvoltage-biasing means connected in parallel to said make and breakcontacts and being provided with an auxiliary switching reactor designedto have an increased resistance when switching in said make and breakcontacts, said auxiliary reactor having a magnet core and an additionalbiasing winding arranged on said core so as to have a slight leakage,and an auxiliary contact device for bridging said additional windingduring the opening of said make and break contacts.

10. A current converting arrangement comprising a switching devicehaving mechanically operated make and break contacts, means forsimultaneously influencing the current and voltage across the switchinggap, said means comprising a self-saturating switching reactorseries-connected to said make and break contacts for decreasing the'current intensities in the neighborhood of the passage of the currentthrough its zero value and voltage-biasing means connected in parallelto said make and break contacts and being provided with a variableauxiliary impedance designed to have an increased impedance value whenswitching in said make and break contacts, a parallel path containingcurrent-limiting impedances. said path being arranged in parallel tosaid make and break contacts in order to reduce the voltage prevailingacross the switching gap between said contacts, and means for connectingsaid parallel path with said make and break contacts shortly beforetheir closure.

11. A current converting arrangement comprising a switching devicehaving mechanically operated make and break contacts, means forsimultaneously influencing the current and voltage across the switchinggap, said means comprising a self-saturating switching reactorseries-connected to said make and break contacts for decreasing thecurrent intensities in the neighborhood of the passage of the currentthrough its zero value and voltage-biasing means connected in parallelto said make and break contacts and being provided with a variableauxiliary impedance designed to have an increased impedance value whenswitching in said make and break contacts, a parallel path containingcurrent-limiting impedances, said path being arranged in parallel tosaid make and break contacts in order to reduce the voltage prevailingacross the switching gap between said contacts, an auxiliary contactdevice for closing said parallel path shortly before the closure of saidmake and break contacts, and means for operating said auxiliary contactdevice in synchronism with said switching device.

12. A converting arrangement comprising a switching device havingmechanically operated contacts. means for simultaneously influencing thecurrent and voltage across the switching gap, said means consisting of acurrent-biasing selfsaturating switching reactor series-connected tosaid contacts and of a voltage-biasing path parallel-connected to saidcontacts, said means being further provided with a variable auxiliaryimpedance having a high impedance value when closing said contacts, asecond parallel path including current-limiting devices and beingdirectly parallel-connected to the make and break contacts in order toreduce the voltage prevailing across the switching gap between saidcontacts, said second parallel path containing a grid controlleddischarge tube, an auxiliary current source connected in the gridcircuit of said tube for supplying a blocking voltage to said grid, anauxiliary contact device connected with said grid circuit so as todiminish when operated said grid voltage in order to allow a currentflow through said tube, and means for operating said auxiliary contactdevice in synchronism with said switching device so as to be actuatedshortly before the closure of the contacts of said switching device.

13. A converting arrangement comprising a switching device havingmechanically operated make and break contacts, means for simultaneouslyinfluencing the current and voltage across the switching gap, said meansconsisting of a self-saturating switching reactor series-connected tothe make and break contacts and of a voltage-biasing pathparallel-connected to said make and break contacts, and being providedwith a variable auxiliary impedance having a high impedance value whenclosing the make and break contacts, an automatic device for bridgingsaid make and break contacts shortly before their closure through asecond parallel path including current-limiting impedances and beingdirectly parallel-connected to said make and break contacts in order toreduce the voltage prevailing across the switching gap. said bridgingdevice comprising a grid controlled discharge tube, an ohmic resistanceseries-connected with said tube for protecting said tube againstoverload in case of disturbances, and means for controlling the gridvoltage of said tube in dependency upon the operation of said make andbreak contacts.

14. A converting arrangement comprising a switching device havingmechanically operated make and break contacts, means for simultaneouslyinfluencing the current and voltage across the switching gap, said meansconsisting of a self-saturating switching reactor series-connected tosaid make and break contacts and of a cur- (iii rent pathparallel-connected to the make and break contacts, and being providedwith a variable auxiliary impedance having a high impedance value whenclosing said make and break contacts, a device for bridging said makeand break contacts shortly before their closure through a secondparallel path including ourrent-limiting devices and being directlyparallelconnected to said make and break contacts in order to reduce thevoltage prevailing across the switching gap, said bridging devicecomprising a grid controlled discharge tube, a parallel-connectiondisposed in series with said tube and including a condenser and an ohmicresistor for protecting said tube against overload in case ofdisturbances, and means for controlling said tube in dependency upon theoperation of said make and break contacts.

15. A converting arrangement comprising a switching device havingmechanically operated make and break contacts, means for simultaneouslyinfluencing the current and voltage across the switching gap, said meansconsisting of a self-saturating switching reactor series-connected tosaid make and break contacts and of a current path parallel-connected tosaid make and break contacts, and being provided with an auxiliaryswitchingein reactor having a high resistance when closing said make andbreak contacts, a device for bridging said make and break contactsshortly before their closure through a second parallel path includingcurrent-limiting devices and being directly parallel-connected to saidmake and break contacts in order to reduce the voltage prevailing acrossthe switching gap, a grid controlled discharge tube arranged in saidsecond parallel path, an auxiliary switching reactor having a mainwinding series-connected with said tube and a magnet core designed tobecome unsaturated at low current intensities near the zero value, abiasing winding on said core, and an energizing circuit connected withsaid biasing winding, said energizing current being adapted to supplysaid biasing winding with a current acting in opposition to the currentflowing through said tube and magnetizing said core to such an extentbeyond itssaturation point that said current flowing through said tubeduring normal operation does not cause said. magnetization to drop belowsaid saturation point.

16. A converting arrangement comprising a switching device havingmechanically operated main contacts, means for simultaneouslyinfluencing the current and voltage across the switch ing gap, saidmeans consisting of a self-saturating switching reactor series-connectedto said contacts and of a current path parallel-connected to saidcontacts, and being provided with a variable auxiliary impedance havinga high impedance value when closing said contacts, an impedancearrangement disposed in parallel to said contacts and designed to bridgethe switching gap shortly before each closure of said contacts, anauxiliary contact device for controlling said bridging arrangement, saidcontact device consisting of a contact pin movably disposed in a bore ofa stationary contact of said main contacts so as to protrude from thecontact surface of said stationary main contact in order to cooperatewith the movable countercontact of said stationary main contact, springmeans for holding said pin in said protruding position, and anadjustable stop for securing said position.

17. A' converting arrangement comprising a switching device havingmechanically operated main contacts, means for simultaneouslyinfluencing the current and voltage across the switching gap, said meansconsisting of a self-saturating switching reactor'series-connected tosaid contacts and of a current path parallel-connected to 5 saidcontacts, and being provided with a variable auxiliary impedance havinga high impedance value when closing said contacts, an impedancearrangement disposed in parallel to said contacts and designed to bridgethe switching gap shortly before each closure of said contacts, anauxiliary contact device for controlling said bridging arrangement, saidauxiliary contact device having a pin movably arranged in a bore of astationary main contact so as to protrude from said contact in order tocooperate with the movable countercontact of said stationary maincontact, a pistonshaped sleeve movably disposed on said pin andconnected with said pin by a spring and an adjustable stop arrangementfor limiting the rein-- tive movements between said sleeve and said pin,a stationary air cylinder surrounding said sleeve and designed fordampening the movements of said sleeve, and a spring disposed betweensaid cylinder and said sleeve for holding said sleeve and said pin inoperative position.

18. With a device for opening and closing an alternating current circuitat a moment of predetermined phase position with respect to the cycle ofsaid current, in combination, voltage-biasing means connected inparallel to said device for reducing the increase of the operatingvoltage recurring at the opening moment across said device, aninductance coil connected in a circuit including in series said deviceand said means, said coil being provided with a core of ferromagneticmaterial having a high permeability and a magnetization curve with asharp saturation bend, a biasing winding disposed on said core, and anenergizing circuit connected with said winding and adapted to cause adesaturating bias of said core shortly before the closing moment of saiddevice, thereby abruptly increasing the inductance of said coil.

19. With a contact device for opening and closing an alternating currentcircuit in a given time relation to the cycle of said current, saiddevice being adjusted to effect said opening at a moment in theneighborhood of the zero value of said current, in combination, meansconnected with said circuit for distorting the curve of said current soas to producea weak current interval including said opening'rnoment,voltage-biasing means connected in parallel to said device for reducingthe increase of the operating voltage recurring at the opening momentacross said device, an inductance coil connected in a circuit includingin series said device and said means, said coil being provided with acore of ferromagnetic material having a high permeability and a somagnetization curve with a sharp saturation bend, a biasing windingdisposed on said core, and an energizing circuit connected with saidwinding and adapted to cause a desaturating bias of said core shortlybefore the closing moment of 05 said device, thereby abruptly increasingthe inductance of said coil.

20. With a contactdevice for periodically opening and closing analternating current circuit in synchronism with the cycle of saidcurrent, said 7 device being adjusted to efl'ect said opening at amoment in the neighborhood of the zero value of said current, incombination, a periodically variable impedance connected in said circuitand designed to increase its impedance value during an intervalincluding said opening moment, a reactive impedance path connected inparallel to the gap of said contact device for decreasing the voltageacross said gap during the opening operation, an inductance coilseries-connected in the circuit including said gap and said parallelpath, said coil being provided with a core of ferromagnetic materialhaving a high permeability and a magnetization curve with a sharp satination bend, a biasing winding disposed on said core, and a biasingcircuit connected with said winding and adapted to control the state ofmagnetization of said core and thereby the inductance of said coilshortly before the contact closing moment of said device in order tocounteract the sparking tendency caused by said parallel path during theclosing operation of said device.

21. With a device for opening and closing an alternating current circuitin a given time relation to the cycle of said current, said device beingadjusted to eifect said opening at a moment in the neighborhood of thezero value of said current, in combination, means connected with saidcircuit for distorting the curve of said current so as to produce a weakcurrent interval including said opening moment, a capacitive pathconnected in parallel to said device for decreasing the voltage acrosssaid device during the opening operation, an inductance coilseries-connected in the circuit including in series said device and saidparallel path, said coil being provided with a core of ferromagneticmaterial having a high permeability and a magnetization curve with asharp saturation bend, a biasing winding disposed on said core, and abiasing circuit connected with said winding and adapted to control thestate of magnetization 01' said core and thereby the inductance of saidcoil shortly before the closing moment of said device in order to impedethe capacitive discharge current of said path during the closingoperation of said device.

22. With a device for opening and closing an allel path, said coil beingprovided with a core of ferromagnetic material having a high permeability and a magnetization curve with a sharp saturation bend, a biasingwinding disposed on said core, and a biasing circuit connected with saidwinding, and adapted to control the state of magnetization of said coreand thereby the inductance of said coil shortly before the closingmoment of said device in order to impede the capacitive dischargecurrent of said path during the closing operation of said device.

23. With a contact device for opening and closing an alternating currentcircuit in a given time relation to the cycle of said current, saiddevice being adjusted to eiiect said opening at a mo ment in theneighborhood of the zero value of said current, in combination, meansconnected with said circuit for distorting the curve of said current soas to produce a weak current interval including said opening moment, areactive path connected in parallel to the gap of said contact devicefor decreasing the voltage across said gap during the opening operationof said device, a variable impedance series-connected in the circuitincluding said gap and said parallel path, controlling means for causingsaid variable impedance to vary its impedance value shortly before thecontact closure of said device so as to counteract the sparking tendencycaused by said parallel path at the closing moment of said device.

24. A current converting arrangement comprising a switching devicehaving periodically operating make and break contacts, a saturablereactor series connected to said contacts for periodically producing aweak current interval at low current intensities, means for controllingsaid reactor to effect said weak current interval in a desired timerelation to the operation of said switching device, a second saturablereactor having one pole connected with one of said contacts and theother pole connected with the other contact of said switching device soas to form part of a parallel circuit with respect to the switching gapbetween said contacts, and means for controlling said second reactor tocause said reactor to increase its reactance shortly before the closingmoment of said contacts.

FLORIS KOPPELM'ANN.

